A U.S. rights group is suing the private security firm, Blackwater, on behalf of victims of a deadly shooting last month in Baghdad.

The Center for Constitutional Rights said Thursday it is filing the suit in a U.S. court for one survivor and the families of three of those who died. The suit accuses Blackwater of murder and war crimes, and it seeks unspecified damages.

Blackwater has not commented on the lawsuit. It has said in the past that its guards were lawfully responding to an attack on a U.S. diplomatic convey they were escorting in the Iraqi capital.

The Iraqi government accuses Blackwater guards of a deliberate, unprovoked shooting spree that killed 17 people in Baghdad September 16.

It is calling on the American contractor to pay $8 million to each of the families of the Iraqis killed.

The incident also is being investigated by the FBI and the U.S. State Department.

U.S. lawmakers have held hearings on the issue of private security firms and the lack of clear legal guidelines that apply to them. Such guards are currently immune from prosecution in Iraq.